Potential Routes for Pathogen Transport to Water

The movement of pathogens to water is dependent upon multiple environmental and transport factors.

Ground Water Contamination by Manure Pathogens

Thomas Harter, Groundwater Hydrologist at University of California-Davis discusses potential for ground water contamination: “While invisible to the human eye, most pathogens are giants of the micro-world … A typical bacterial pathogen is … much too large to fit between the clay or silt particles of many clay, silt, or loam soils…Only in sandy soils, the pore space is indeed large enough to provide ample traveling space for pathogens. Even there, pathogens frequently collide onto grain surfaces where they tend to become permanently attached. Ultimately, most pathogens are strained or filtered out of the water cycle long before reaching groundwater or a stream. Even if pathogens reach an aquifer, the aquifer itself will filter most remaining pathogens over relatively short distances (100 ft – 300 ft)…"

Dan Shelton, Environmental Microbial Safety Lab Research Leader, USDA Agricultural Research Service identifies some important exceptions including: “sandy or rocky soils, which generally allow for greater infiltration, …heavy soils (e.g., clay) containing significant cracks or fissures, or channels created by decayed plant roots or burrowing worms, (creating potential contamination of shallow ground water or tile drains)… and soils/subsoils throughout the Appalachian region derived from limestone geological formations (known as karst). Finally, improper installation of wells can allow for direct contamination of groundwater via the leaching of organisms along the well casing.”

Protozoa and bacterial pathogens are commonly too large to fit between the particles in most soils.
Source: Thomas Harter, University of California-Davis.

Surface Water Contamination by Manure Pathogens

Pathogen contamination of surface water is more common than contamination of groundwater. Direct contact of animals with surface water or runoff from animal housing is a significant risk. Land application sites with high runoff and erosion potential provide an additional potential pathogen connection to surface water. Thus, soil and nutrient conservation practices that minimize runoff and erosion are key BMPs for pathogen risk reduction.

Environmental Factors That Influence Pathogen Survival

Jeanette Thurston-Enriquez, USDA Agricultural Research Service scientist, summarizes environmental factors that reduce the survival of pathogens:

High temperatures. Each pathogen has a different susceptibility but generally high temperatures are very effective in reducing populations.

Time. Bacteria are living organisms, so they can't live forever…

Sunlight. Has a couple of effects on pathogens. It desiccates (reduces moisture levels) them and the UV light also inactivates pathogens…

Desiccation. Is one of the best ways to inactivate pathogens in the environment.

Recommended Resources on Pathogen Transport to Water

Pathogen transport in the environment is summarized in Dr. Jane Frankenberger’s web cast presentation found in the pathogen webcast archive. Additional information on survival time can be found starting on page 25 of USDA NRCS technical note, Waterborne Pathogens in Agricultural Watersheds.